Supplementing water spinach (Ipomoea aquatica) with foliage of Mimosa pigra or Leucaena leucocephala and coconut oil; effects on N retention and enteric methane emissions in growing goats

Nguyen Thi Thu Hong, Nguyen Thi Ngoc Trang¹, Duong Nguyen Khang² and T R Preston³

Angiang University, Vietnam
ntthong@agu.edu.vn
¹ Kiengiang University, Vietnam
² Nong Lam University of Ho Chi Minh City, Vietnam
³ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia

Abstract

Four growing male goats (12.6±1.42kg) were used in a 4*4 Latin square arrangement to compare effect of two factors on feed intake, digestibility, N retention and methane emissions. The first factor was source of tannin (fromMimosa pigra or Leucaena leucocephala); the second factor was coconut oil supplementation with or without at 10g/kg DM intake.

Replacing Leucaena with Mimosa pigra as the supplement to water spinach reduced the DM intake, tended to increase the DM digestibility and N retention (p=0.058 and 0.075), improved the biological value of the N (N retained as % of N digested) and the feed conversion (DM intake/N retention) and reduced the ratio of methane to carbon dioxide in expired breath. By contrast, supplementing the diets with coconut oil led to a reduction in rumen methane but had no effect on performance traits.

It is hypothesized that the improvements in performance traits (N retention and DMI to N conversion ratio) when Mimosa pigra replaced Leucaena were the consequence of the greater rumen bypass characteristics of the protein in Mimosa pigra associated with the increase in energy metabolism efficiency as a consequence of the reduction in rumen methane. In contrast, the coconut oil although effective in reducing rumen methane did not improve performance traits as measured by daily N retention and N retained per unit DM intake. The condensed tannins, present in a 64% higher concentration in Mimosa pigra than in Leucaena, thus appear to confer two benefits on the host animal: (i) an improvement in rumen bypass characteristics of the protein; and (ii) a reduction in the production of rumen methane.

Key words: bypass protein, eructed gas, greenhouse gases, invasive plant, legume, tannins

Introduction

Opportunities in the strategy to reduce greenhouse gas emissions from the livestock are: (i) to increase ruminant animal productivity (Figure 1); and (ii) to reduce rumen production of methane. Feeds rich in condensed tannins can contribute to both these objectives as their reaction with proteins in the rumen potentiates the escape (bypass) of protein from the rumen (Barry and McNabb 1999) with resultant increase in animal productivity (Preston and Leng 1987); condensed tannins also have been shown to act directly to reduce rumen methanogenesis (Woodward et al 2004; Dias-Moreira et al 2013).

Figure 1. Relationship between live weight gain and enteric methane production per unit live weight gain (Klieve and Ouwerkerk 2007)

The objective of the research reported here was to verify the above strategy by feeding a tannin-free foliage (Ipomoea aquatica) as the basal diet of growing goats and testing the effect of two supplementary foliages with different levels of condensed tannins ( Leucaena leucocephala and Mimosa pigra) and of supplementation with coconut oil previously shown to depress rumen methane in ruminants (Liu et al 2011).

Mimosa pigra is an invasive legume that has colonized appreciable areas in Vietnam (Tran Triet et al 2007). However, it has been shown that its nutritive value for goats is high and that this appeared to be linked with the presence of condensed tannins in the foliage (Thu Hong et al 2008; Thu Hong and Lam 2011). Leucaena is known for supporting high growth rates of goats in confinement (Nguyen Thi Hong Nhan 1998).

Material and methods

Location

The experiment was carried out in the farm of An Giang University from January to June 2017.

Experimental animals, treatments and design

Four growing male goats (12.6±1.42kg) were hired from smallholder goat keepers in the area. The trial was designed according to a 2*2 factorial arrangement of four treatments with 4 replications. The experiment was designed with two factors: (i) Mimosa pigra or Leucaena leucocephala as sources of condensed tannin (at approximately 50 g tannin/kg diet DM); and (ii) supplementation with or without coconut oil at 10g/kg DM intake.

Individual treatments were :

WM: Water spinach plus Mimosa

WMC: Water spinach plus Mimosa with coconut oil

WL: Water spinach plus Leucaena

WLC: Water spinach plus Leucaena with coconut oil

Feeds and management

The goats were vaccinated against foot and mouth disease and de-wormed before the start of the experiment. They were individually fed in metabolism cages with free access to water and mineral blocks. New feed was offered daily at 08:00 and 16:00. All treatments included 30g rice bran/day as carrier for the coconut oil.

Branches of Leucaena and Mimosa growing wild in nearby fields were collected every day. Water spinach was grown on plots in the University farm and was harvested after 21 days of regrowth. It was put in the feed trough at an offer level of about 120% of recorded intake. The branches of leucaena and mimosa were tied in bunches suspended above the feed troughs in amounts that would provide approximately 50 g condensed tannin per 1 kg DM intake (Photo 1).

Photo 1. Mimosa pigra growing wild	Photo 2. Suspending the branches of Mimosa pigra to simulate browsing

Each experimental period lasted 20 days. For the first 10 days in each period, the goats were adapted to the new diets. From 11 to 15 days feces and urine were collected, and feeds offered and refused were recorded. The urine was acidified with 10% H₂SO₄ to prevent ammonia-N loss. Samples of feces and urine. and of feeds offered and refused were pooled over the 5-day collection period and refrigerated (-18°C) prior to analysis. On the 15th day of each period of the experiment, the carbon dioxide and methane in eructed gases were measured. The gases were collected in the morning by placing the goats in a glass chamber and after a period of 5 minutes for equilibration with the air in the chamber, the concentrations of methane and carbon dioxide were determined using a Greenhouse Gas Analyzer, model number 908 - 0011. There was rest periods of 5 days between experimental periods, when the goats were feed only grass.

The samples of feed offered and refused and of feces were analysed by AOAC (1990) methods for: dry matter (DM) by drying at 105⁰C for 24h; organic matter (OM) by ashing at 550⁰C for 4h; and crude protein (CP) by Kjeldahl technique. Neutral detergent fibre (NDF) and acid detergent fiber (ADF) were analysed using the method of Van Soest and Robertson (1985). The condensed tannin content of feeds was determined by the Lowenthal method (AOAC 1936).

Statistical analysis

The data were analyzed using the general linear model in the ANOVA program of the Minitab software release 16.20. Sources of variation in the model were: source of supplementary foliage (Leucaena or Mimosa pigra), supplementation with coconut oil, interaction foliage*coconut oil, animals, periods and error.

Results

Condensed tannin was 64% higher in Mimosa pigra than in Leucaena; but protein levels were similar (Table 1). There was no tannin in water spinach. Levels of fiber (NDF and ADF) were higher in Mimosa pigra than in Leucaena.

Replacing Leucaena with Mimosa pigra as the supplement to water spinach reduced the DM intake, tended to increase the DM digestibility and N retention (p=0.058 and 0.075), improved the biological value of the N (Figure 1) and the feed conversion (DM intake/N retention) and reduced the ratio of methane to carbon dioxide in expired breath (Table 2). By contrast, supplementing the diets with coconut oil led to a reduction in rumen methane but had no effect on performance traits.

Figure 2. DM intake per unit N retention in goats fed water spinach supplemented with Leucaena or Mimosa pigra, or with coconut oil

Figure 3. Relationship between methane: carbon dioxide ratio in eructed rumen gas and nitrogen retention in goats fed diets with varying concentrations of condensed tannins

Figure 4. Relationship between methane: carbon dioxide ratio in eructed rumen gas and feed conversion (ratio of DM intake per unit N retained) in goats fed diets with varying concentrations of condensed tannins

Discussion

It is hypothesized that the improvements in performance traits (N retention and DMI to N conversion ratio) when Mimosa pigra replaced Leucaena were the consequence of the increase in energy metabolism efficiency as a consequence of the reduction in rumen methane (Figure 4). In contrast, the coconut oil although effective in reducing rumen methane did not improve performance traits as measured by daily N retention and N retained per unit DM intake. The condensed tannins, present in a 64% higher concentration in Mimosa pigra than in Leucaena, thus appear to confer two benefits on the host animal: (i) an improvement in rumen bypass characteristics of the protein; and (ii) a reduction in the rumen methane.

Conclusions

• Replacing Leucaena with Mimosa pigra, as the supplement to water spinach fed to goats, reduced the DM intake, tended to increase the DM digestibility and N retention (p=0.058 and 0.075), improved the biological value of the N (N retained as % of N digested) and the feed conversion (DM intake/N retention) and reduced the ratio of methane to carbon dioxide in expired breath.
  
  
• Supplementing the diets with coconut oil led to a reduction in rumen methane but had no effect on performance traits.

Acknowledgments

We wish to thank the MEKARN II project, financed by Sida, for funding this study.

References

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Received 27 September 2018; Accepted 14 November 2018; Published 2 December 2018

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